Automatic telephone system



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- UNITED STATES.

PATENT on-Ice annular I. uncann or cnronao, mnniors atr'roauvrrc eramnona srs'rax Original application fled Iebmry 17, 1081, Serial No. 445,781. Renewed November 8, 1926. Original llo. 1,887,844, dated Kay 10, 1887. Application for reissue iiled August 84, 1827. .SeriaI No. 816,847.

.particularly adapted to a system that includes a main exchange, having a plurality 6 of branch oifices tributary to 1t.

More specifically, the invention relates to an improved method and apparatus for permitting either a callin party in the main exchange or 8. called so scriber in a branch exchange to transfer the call to another dc sired subscriber in the branch exchange. Other systems have been invented which embody certain arrangements of this nature, but herein-are provlded many new features together with improvements in the structure of such a system.

Among the important features of the invention an arran ement is provided Whereby, after a-call as been transferred from one branch exchange subscriber to another the three parties may remain on the line for a conference, and as soon as this is terminated either part at the branch exchange may release the ot er by dialing the di it 1; or should this feature not be desira le the first called party ma be automatically released upon t e secon called party answering.

Another important feature is the sion of means whereby if the branc exchange subscriber upon receiving a call should desire to obtain information from an have special services of an operator if they so desire. I These and other features of the invention will be fully disclosed hereinafter.

rovi- 1 drawings.

ig. 1" shows the manner in which the different sheets of drawings are placed for a complete view of the system.

In Fig. 2 the apparatus at the main exchange is shown diagrammatically and consists of a subscriber s substation A, having agreselector or rotary lineswitch C indivi 4 ual thereto, and which has access in common with a plurality of other similar lineswitches to first selectors ofthe standard Keith-Erickson two wire class, one of which is shown at E. These selectors have access to selector repeaters off a certain level of bank contacts. The selector repeaters may be of any well known two wire type such as that shown in Fig. 1 of the patent to Emil J acobsen No. 1,332,217, issued March 2, 1920.

' These selector repeaters have access to trunk features of the present invention. The trunk I line comprising conductors 26 and 27 is shown terminating in such a dual switch, Figs; 3 and 4.

In Figs. 5, 6, 11 and 13 ordinary selector switches of the Keith-Erickson two wire type are shown, the circuits of which have been modified to operate in this system.

Figs. 7, 8, and 9 show connector switches of the well known Strowger type which also have been modified as will appear fully hereinafter.

Fig. 10, shows an improvement that has been designed for controlling a large number of oil normal springs when the weight of the switch shaft is inadequate to shift them.

Fig. .12-shows an operators cord-pair.

Figs. 14 and 15 show certain details of the resent invention which will be described lly'hereinafter. While in the drawings a plurality of batteries have been shown, it will be understood that there is preferably, but one battery'having its negative pole grounded for each exchange.

The operation of this improved system will now be described in general, reference being bad to Fig. 1. v Let us consider first what is shown on the left of the dotted line, where is indicated the ap aratus in the main exchange. The subscribers lines shown in the upper left hand corner of the sheet are provided at the exchange with individual rotary line switches having common access to a group of selector switches, one of which is indicorresponding to. ten levels.

cated by the square at the left of the sheet. This is an ordinary Strowger switch of the usual mechanical construction. The banks of which are indicated by 10 heavy lines these selector switches terminate selector repeaters one of which is shown immediately to the right of the first selector. Another level of the selector switches has access to local second selectors shown diagrammatically at the bottom square on the left; and as shown'one level of these selectors go to local connectors which have access to main exchange subscribers lines. The selector repeaters have access to trunk lines going to the branch exchanges and terminating there in dual'selectors, one of which is shown terminating in the dual selector switches 1n the branch exchange. The switches in the a branch exchange shown on the right of the dotted line consist of two groups, those used in a local call and those used in an incoming call. The dual incoming selectors have access to incoming second selectors ofi certain levels of their bank contacts. These second selectors have access to incoming connectors which are adapted to connect with local subscribers lines. The local subscribers, shown at upper extremity of the drawin have each an individual rota line sw1tch which has access to local branc exchange first selectors. A certain level of these selectors, the second as shown, is multipled-into the second level of the incoming dual selectors, this is for a ecial purpose as will later appear. Other evels have access to local second selectors, while the 0 level is used for outgoing calls to the main exchange.

The process of settin up connections will now be briefi consi ered. Suppose first that a subscri r in main exchange wishes to connect with a subscriber in the branch exchan When the receiver is removed at the ca ng stationthe rotaryline switch individual thereto operates to select an idle first selector. The calling subscriber will tically' to the sixth One level of,

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thereupon dial the di 't which'corresponds to the level leading t t e selector re ater and which in this case is the digit 7. en this digit is called .the selector steps to the seventh level and operatesto automatically select an idle selector re eater. The calling subscriber may now cal the digit 6 whereupon the selector repeater will operate verevel and rotate to find an idle trunk line going to the branch exchange and terminating there in a dual selector. The calling party ma now call the remaining four digits of the esired branch exchange subscribers number whereupon the connection will be completed in the usual manner. If it should be found, upon the called subscriber answering, that another branch exchange subscriber was wanted, the called party can by callin that local subscribers number, connect wit that subscriber by means of the other element of the dual selector. 'When this party answers the three subscribers may remain on the line for a conference or the first (or second) called party ma han up leaving the second (or first) cal ed an original calling parties in communication with each other. The call may be again assed, if necessary, as many times as desira lg Let us consider also the case of where the called party desires to communicate with another subscriber in the branch exchan c. He will dial the digit 2 which will cause t e other dual selector element to step to the level and connect with the holdin trunk which is multipled into the secon level of the local branch exchange first selectors. The called subscriber may now release the connection to himself and use the local branch exchange switches'to call another party. After obtainin whatever in formation he desires he may dial the digit 2 which will cause the local first selector to step to the second level and then rotate into connection with the holding trunk. The called party is now in communication with the original calling party again and the call may be passed as in thecase first mentioned.

The local branch exchange subscribers by dialing 0 operate a first selector vertically to the tenth level whereu n the switch automatically rotates to fin an idle two way trunk going to the main exchan e. As soon as this is found the line switc associated therewith in the main exchange operates to select an idle first selector whereafter the call is completed in the usual manner to a main exchange subscriber.

Special service is also provided for certain subscribers in the branch exchange. By removing their receivers and dialing 1 the first selector under their control is stepped up a connection fromthe calling line either manually or automatically in a well-known manner.

. Having described the general objects of this invention and the general manner of obtaining these objects the detailed operation of a system embodying those improvements will now be considered.

'For this purpose it will be assumed that asubscriber at substation A inthe main exchan e desires to call the branch exchan e subscri er at substation P and that the said calling subscriber has, by operating his calling device for a series of di its seized the two way trunk line comprising conductors 26 and 27 by means of the selector repeater C, in a well known manner.

When the call is thus extended to the trunk line, a circuit is completed for the line relay 56 of the main selector F over the two sides of thecalling line in series. Relay 56, upon energizing, closes a circuit at armature 91 and its front contact for' the slow acting release relay 57 which in turn energizes to pre are a circuit for the vertical magnet an to place ground on conductor 36 at armature 93 and its front contact. This ground extends over the release trunk conductor 36 through the winding of relay 34 to battery. The latter relay, on energizing, places ground on the multipled release trunk in the banks of local selector switches in which this incoming trunk is accessible.

Now, when the calling device of the calling subscriber is operated to open the line circuit a number of times in accordance With a digit of the called number, the line relay of the selector repeater will produce a corresponding series of interruptions in the circuit of the line relay 56 of the main selector F. Upon each retraction of its armature the line relay 56 closes a circuit extending from ground G, by way of armature 91 and its back contact, conductor 137, armature 220 and its resting contact, conductor 146, armature 104 and its back contact, armature 94 and its front contact, through the winding of the slow acting relay 58,conductor 139, back contact and armature 215, conductor 141, armature 155 and its back contact, back contact and armature 89, and thence through the winding of the vertical magnet 64 to battery. Relay 58 energizes in series with the vertical magnet, and being a-slow acting relay, maintains its armature attracted during the operation of the switch, Magnet 64 operates to raise the wipers 112- 115, inclusive, step by'step until they are placed opposite some level of bank contacts,-

in which are terminated trunk lines leading to the branch exchange second selector switches.

As soon as the wipers leave their normal position the spring 119 is shifted into engageme'nt with its frontcontact thereby completmg a'circuitdfor magnet 67. The oper- To continue,'when the ofi normal springs are 0 erated' a circuit is com leted extending rom ground G, throug armature 93 and its-front contact, armature 96 and its front contact, armature 87 and its back contact, armature 159 and its resting contact, ofl" normal springs 116, and thence through the winding of the interrupterrelay 59 to battery. Relay 59 energizes to prepare the rotary magnet circuit at armature 100 and locks itself to ground at armature 99. The slow actin relay 58 falls back an instant after the impulses to the vertical magnet have ceased. When this occurs a circuit is completed for the rotary magnet 65 extending from ground G byway of armature 93 and its front contact, armature 96 and its back contact, armature 100 and front contact, and through the winding of the rotary magnet 65 to battery. Magnet 65 operates to rotate the wipers 112 to 115, inclusive, into engagement with the first set of contacts in the selected level and at the same time opens the locking circuit of relay 59 which deenergizes, breaking the circuit of the rotary magnet which deenergizes also. When magnet 65 denergizes it prepares a new circuit for the interrupter relay 59 extending from the test wiper 112, through armature 88 and its resting contact, back contact and armature 160, armature 159 and its back contact, off normal springs 116, and thence through the winding of relay 59 to battery. Now, if the first trunk line of this level, on the test contact of which the wiper 112 now rests, is busy a ground potential will be present thereon and relay 59 will energize over the above traced circuit. On energizing, relay 59 operatesas before to close the rotary magnet circuit. Magnet 65 operates to advance the. switch wipers into engagement with the set of bank contacts associated with the next trunk line and to again break the circuit of the interrupter relay, which relay on deenergizing breaks the rotary magnet circuit. This alternate operation of relay 59 and magnet 65 continues until an idle trunk line is found which, it will be assumed, is the trunk line comprising the conductors 250 to 253, inclusive, and which terminates in the selector H, Fig. 5. When the switch wipers are rotated into engagement with this trunk line no ground will be present on the test contact engaged by the wiper 112 and relay 59 will notbe again energized to close the rotary magnet circuit. It will be noticed that during the rotation of the switch in search of an idle trunk line the switching relay was short circuited by ground on the successive busy test contacts through wiper 112, now, however, when an idle trunk line is reached, the relay 55 is no longer short circuited and hence it will energize over a circuit extending from ground G through armature 93 and its front contact, through the winding of relay 55, back contact and armature 160, armature 159 and its back contact, oft normal springs 116,

and thence through the winding of relay- 59 to battery. Relay 55 is of comparatively high resistance and does not permit the relay 59 to operativcly energize in series with it. Upon energizing, relay 55 opens the vertical magnet circuitat armature 89-, connects ground to the wiper 112 at armature S8, prepares the circuit of the wiper cut on relay 63 at armature 86, and completes a repeating circuit at armature 90. This repeating circuit extends from ground G, by way of armature 92 and its front contact, armature 77 and its-back contact, back contact and armature 72, conductor 127, armature 194 and its back contact, back contact and armature 199, conductor 121, front contact and armature 90, armature 158 and its back contact, through the winding of he slow acting series relay 61, wiper 113, bank contact 258, conductor 251, armature 300 and its resting contact, and through the winding of the line relay 301 of the selector H to battery. The line relay 301 energizes in series with relay 61 and said relays 301 and 61 actuate over this circuit and completes a circuit in the usual manner for the slow release relay 302. This relay on energizing prepares the vertical magnet .circuit at armature 3-11 and its front contact. The actuation of relay 61 disables relay 63.

The calling main exchange subscriber may now operate his calling device in accordance kll with the next digit of the desired number; A series of interruptions is thereby produced in the circuit of the line relay 56 of the main selector F which relay operates and at each retraction of its armature 92 opens the previously traced circuit for the line relay 301 of the selector H. The latter relay at each deenergization sends a current impulse through the slow acting relay 304 and the vertical magnet 307 in series to battery By the operation of the vertical magnet the selector shaft is raised step by step until the wipers 310-313, inclusive, stand opposite the desired lever of bank contacts. The slow acting relay 304 is energized in series with the vertical ma et, retains its armature attracted throughout the vertical and 315 completes a circuit for the interrupter relay 305. Upon energizing relay 305 prepares a circuit for the rotary magnet 308 at armature 317, and at armature 318 establishes a locking circuit for itself. At the end of the vertical operation of the switch the slow acting relay 304 is deenergizcd and closes the circuit of the rotary magnet, which is thereupon energized to advance the wipers 310-313, incluslve, into engagement with the first set of bank contacts in the level opposite which they were raised. The rotary magnet also breaks the circuit of the interrupter relay 305, which is accordingly deenergized to break the circuit of the rotary magnet, which thereupon deenergizes also and again closes its interrupter contact. The operation now depends upon whether the test contact with which the test wiper 310 is now in engagement is or is not busy. If this test contact is busy it will have a ground potential on it, and the interrupter relay 305 will be energized again over a circuit which extends from the said grounded test contact, by way of the test wiper 310, armature 320 and its back contact, the interrupter contact 322 of the rotary magnet, the 011' normal springs 314, and the winding of the interrupter relay 305 to battery. The interrupting relay will therefore energize to again close the circuit of the rotary magnet 308, which will oper-- ate to advance the switch wipers into engagement with the next set of bank contacts. This operation by which the interrupter relay and the rotary magnet are alternately energized and deenergized will continue as long as the test wiper 310 engages busy or grounded test contacts. In the present case it will be assumed that the trunk line shown in the drawings is the first idle trunk line and when therefore, the test wiper 310 arrives at test contact 325 and the rotary magnet is deenergized, the interrupter relay 305 will not be energized, but

instead, the switching relay 306, which has hitherto been short circuited will be operated by current flowing over the following path: grounded conductor 250, winding of the switching relay 306, interrupter contact 322 of the rotary magnet, ofi normal springs 314, and the winding of the interrupter relay 305 to battery. Owing to the high resistance of the switching relay 306, the interrupter relay is not operated. Upon energizing, relay 306 disconnects the incoming dialing conductor 251 from the winding of the line relay 301 and extends it by way of armature 300 and its front contact, wiper 311, bank contact 326, conductor .328, arma ture 366 and its back contact, back contact 1 and armature 361, and through the winding relay 306 on energizing, also extended the release trunk conductor 250 by way of front contact and armature 320, W1 er 310, bank contact 325, conductor 327, an through the winding of relay 351 to battery. This latter relay energizes and repares the circuit of the vertical magnet of the connector J.

It might have happened however, that all the trunk lines in the selected level were busy. Under these conditions the rotation of the switch H would" continue until the springs 310 and 311 were closed which occurs on the eleventh rotary step of the switch, being operated by the cam on the switch shaft in a well known manner. These springs on operating, connect the dialing conductor 251 direct through the winding of the line relay 301 to batteryand at the same time place a busy tone on the upper line conductor 252. This busy tone is audible to the calling subscriber over a circuit that extends over conductor 252, bank contact 256, wiper 114, armature 108 and its back contact, armature 85 and its front contact and thence over the line of the calling subscriber. -Upon hearing this tone, the calling subscriber will replace his receiveron the switchhook knowing that for the present he is unable to obtain his desired connection. The replacement of the receiver at the calling substation initiates the release of the operated switches in a manner to be described hereinafter.

Returning now to the operation of the system after the trunk line comprising the conductors 328-330, inclusive, has been seized; the calling subscriber may now operate his calling device for the next digit of the called subscribers number, thereby causing the line relay 56 to again operate. in response to the said impulses and repeat them to the line relay 350 of the connector J. At each'retraction of its armature 356, the line relay 350 completes a circuit for the vertical magnet 372 in series with the slow acting private control relay 352, which relay maintains its armature attracted during these impulses. Magnet 372 operates to raise the switch shaft step by step until the wipers 377-380, inclusive, stand opposite the desired level of bank On energizing, the slow acting relay 352 completes a circuit for the private magnet 371 at armature 358 in multiple with relay 353. The operation of relay 353 is at this time without function. The private magnet, however, controls the sideswitch in the usual manner, and uponthe deenergization of the slow acting private control relay 352 contacts.

I permits the sideswitch wipers to advance to their second position.

The calling subscriber maynow operate his callin device in accordance with the final digit in the called number, thereby producing a series of interruptions in the circuit of the line relay 56 which repeats them to the line relay 350 as before. Now, however, this latter relay transmits a corresponding number of impulses to the rotary magnet 373. The circuit being traced from ground G" by way of armature 356 and its back contact, armature 357 and its front contact, through the winding of the private control relay 352 armature 362 and its back contact, and through the winding of the rotary magnet 373, and sideswitch wiper in the second fposition to battery. By the operation 0 the rotary magnet, in response to the impulses of current which it receives, the switch shaft is rotated step by step, until the wipers 37 7- 380, inclusive, are brou ht into engagement with the bank contacts in which the desired described, was busy. Under these conditions there would be a ground potential on the test contacts 381 and 382 which are engaged by the test wipers 377 and 378 with the result that the private ma net 371will not deenergize when the circuit is broken for its inner winding at armature 358 but is maintained operated over a test circuit extending as follows: ground on test contact 382, test wiper 37 8, sideswitch wiper in the second position, and through the outer winding of the private magnet 371 to battery. Also relay 354 is energized over the following circuit: grounded test contact 381, test wiper 377, spring 365, armature 359 and its back contact, through the winding of relay 354 and the sideswitch wiper in the second position to battery. On energizing, relay 354 closes a locking circuit for itself and the private magnet independent of the test wipers 377 and 378, this circuit extending from ground G oif normal springs 375, armature 364 and its front contacts, inner winding of the private magnet to battery and in multiple with this last traced circuit by way of armature 359 and its back contact, through the winding of relay 354 and the sideswitch wiper in the second position to-battery. Relay 354 opens the rotary magnet circuit at armature 362, opens the circuit of the line relay 350 at armature 361, and places the tone from the busy machine T on the upper heavy talking conductor 329. When the circuit of relay 350 is opened relay 61 in the main selector F, in series with the dialing circuit, deenergizes and completes the circuit for the wiper cut on relay 63. This circuit may be traced from ground G by way of front contact of'the calhng subscriber by the operation of the relay 354 over a circuit which extends from the busy machine T by way of armature 363, conductor 329, bank contact 323,

and wiper 312, front contact and armature 321, conductor 252, bank contact 256, wiper 114, armature 108 and its front contact, armature 105 and its back contact and thence through the lower winding of the ring cut off relay 62 to battery. This operation will induce a current corresponding to the busy tone in the upper winding of ring out off relay 62 from whence it flows over conductor 121 through the lower winding of the back bridge relay 51, oil normal springs 48, back contact and armature 69, through the condenser and thence over the lower line conductor to the substation A and back through the upper winding of relay 51 to battery. This tone will inform the calling subscriber at substation A that the line of the subscriber at snbstation,P is for the time being, inaccessible, and he will replace his a receiver. The disconnection of the various switches will be described hereinafter.

Having thus described the operation of the connector J when the called line is busy, it will now be assumed that when the connection therewith was attempted the line of the substation P was idle. Under these circumstances, when the slow acting relay 352 deenergizes at the end of the final series of impulses the private magnet 371 is deenergized also and the sideswitch passes to the third position. By the advance of the sideswitch wipers to their third position two circuits are closed in multiple. One extending from ground G", sideswitch wiper in the third position, through the test wiper 378, test contact 382, private normal conductor 385, springs 386, conductor 387, the winding of switching relay 407 of the lineswitch C, and the winding of the stepping magnet to battery. In parallel with this circuit one is also closed for the busy lamp 452 thereby notifying an operator who has access to the line of the subscriber at substation P that this line is now busy. The current flow in this circuit serves to energize the switching this line busy. When the sideswitch steps to the third position another circuit is also completed in multiple with the above for the wiper cut on relay 355 in an obvious manner. On energizing, relay 355 prepares the ringing circuit at armatures 367 and 368, and at armature 366 opens the circuit of the line relay 350. As before, as soon as the circuit to the line relay 350 is broken the slow acting series relay 61 in the main selector F deenergizes. A circuit is thereby completed extending from ground G front contact and armature 86, armature 103 and its back contact, and through the winding of the wiper cut on relay 63 to battery. Relay 61 on deenergizing, also breaks the circuit of v the slow acting relay 60 which relay deenergizes a short interval afterwards. During this interval a distinctive tone from the tone machine T is placed on the calling subscribers line conductor thereby notifying him that his call is proceeding satisfactorily. Relay 63 upon energizing, completes the ringing circuit for the called subscribers telephone which extends from the ungrounded pole of generator V, over conductor 245, conductor 145,. back contact and armature 107, armature 111 and its front contact,.

wiper 115, bank contact 257, conductor 253, armature 260 and its front contact, wiper 313', bank contact324, conductor 330, armature 368 and its front contact, wiper 380, bank contact 384, line conductors 393 and 401 of the substation P, through the ringer ring cut off relay which is audible to the calling subscriber, thereby notifying him that his call is proceeding satisfactorily.

The ringing of the called substation P will continue intermittently in the ordinary manneruntil the subscriber thereat removes his receiver. When this occurs a circuit for di; rect current is completed over the previously traced ringing circuit through the switchhook springs, transmitter, and receiver of'the called substation for the ring cutoff relay 62, which, while it is adjusted not to respond to alternating current, will operate over this circuits. On energizing, relay 62 disconnects the ringing current from the called line at armature 107 at the same time connects the talking circuit to the windings of the back "bridge relay 51 at armatures 105 and 107 and-their front contacts, and locks itself energi'zed at armature 106 and its front contact. A circuit is now completed extending from ground G"? off normal springs 118 and its working contact, front contact and armature 106, conductor 121, [throu h the lower winding of the back bridge re ay 51, working contact of 05 normal spring 48 and the said spring, front contact and armature 107, and then over the previouslytraced ringing circuit back to wiper 114, armature 108 and its front contact, armature 105 and its front contact, working contact of off nor-. mal s ring 49 and the said s ring, and throug t e upper winding 0 the back bridge relay 51 to battery. Relay 51 will therefore energize, completing a circuit extending from ground G by way of armature 70 and its front contact, spring 117 of key K and its resting contact, conductor 132, armature 200 and its resting contact, conductor 131, resting contact of spring 118 and the said spring, and through the winding of the slow acting relay 52 to battery. Relay 52 will attract its armatures and at armature 73 complete the circuit of relay 53 and at armature 76 place ground on conductor 38 extending through the winding-of relay 25 to battery. On energizing, this latter relay reverses the connections of the line relay 56 with regard to the trunk conductors 26 and 27 thereby reversing the battery back to the calling line for any desired purpose. The energizationof relay 53 simply prepares the o erating circuits of the auxiliary selector GB The calling and called subscribers may now converse over the heavy conductors in the usual manner.

When the conversation is completed the connection may be released by the hanging up of the receiver at the calling substation. Relay 56 will therefore deenergize opening the circuit of the slow actin release relay 57, which deenergizes also. his latter relay on deenergizmg removes ground from .the release trunk conductor 36 and at the same times closes a circuit for the release magnet extending from ground C} by way of armature 93 and its back contact ofl. normal springs 117, and through the winding of the release magnet 66 to battery. The switch F will be immediately released by the energization of magnet 66 and as the holding circuit for the slowv acting release relay 351 of the connector J and the switching relay 306 of the selector H has been opened b the deenergization, of relay 57 each of these relays will accordingly deenergize. .Relay 351 completes a clrcuit extending from ground G,-by way of armature 399 and its back contact, ofi' normal springs 374, and through the winding of the release magnet 369 to attery, and relay 306 completes a circuit extending from ground G", by way of armature 308 and its back contact, back contact and armature 340, armature 341, and its back contact, 05 normal springs 315, and then throu h the winding ofthe release magnet 342 to attery. Mag- ,nets 369 and 342 will operate to restore their respective switches to their normal position. Thus, in the above described manner all the switches will be restored to'normal.

Let us now assume that the calling subscriber who has directed the extension of the previously described connection, desires to talk with some other subscriber in the branch exchange. In order to do this he will merely dial the local branch exchange number of that subscriber, thereby operatin the auxiliary selector G to select an idle ranch exchange second selector, after which the call will proceed in the ordinary manner.

This operation will now be described. When the calling device of the substation A is operated a series of interruptions is produced in the circuit of the line relay 56. At each retraction of its armature 91, a circuit is completed extending from ground G, by way of armature 91 and its back contact, conductor 137, armature 220 and its back contact, conductor 146, armature 104 and its, resting contact, armature 94 and its front contact, armature 97 and its back contact, conductor 140, through the winding of slow acting series relay 171, armature 231and its back contact, armature 211 and its back contact, and through the windin of the vertical magnet 177 to battery. t will be noticed that this circuit was also operative when the main selector was operated in the original connection but under these conditions the series relay 58 is adjusted to pull up first breaking the above traced circuit at armature 97 whereupon it was then ineffective. Relay 56 also completes another circuit at each retraction of its.

armature 92 extending from ground G by way of armature 92 and its back contact, front contact and armature 95, conductor 138, and thence through the winding of slow acting relay 170 to battery. This relay energizcs, and at armature 213 places ground on conductor 136, and at armature 212 and its front contact places ground on conductor 151, extending by way of armature 110 and its front contact, off normal springs 117, and through the winding of release magnet 66 to battery. Magnet 66 operates to lock itself to ground on conductor 136 at armature 157, to open the operating and repeating circuits of the main selector F and to restore the said switch to its normal position. The slow acting series relay 171 energizes in series with the vertical magnet 177 and opens the operating circuits of the main selector F at armature 215. Magnet level of bank contacts in which trunk lines leading to selectors are terminated, Upon the wipers leaving their normal position the circuit of the ofi normal magnet 180 is com plcted and it operates to shift the springs 240, 241,242, 245, and 246 into their oil normal position in a similar manner to magnet 67. A circuit is thereby completed extending from ground G by way of armature 93 and its front contact, conductor 36, conductor 123, armature 216 and its front contact, armature 234 and its back contact, ofi normal springs 240, and thence through the winding of relay 172 to battery. Rela 172 ener 'zes over this circuit locks itmlf to groun at armature 218 and its front contact, byway of the interrupter springs 181 of the rotary magnet 178, and at armature 219 and its front contact prepares the rotary magnet circuit. The release magnet 66 of the main selector F remains energized the wi ers 235-238, inclusive,

set of ank contacts in the selected level and V switch associated until the slow acting relay 170 deener 'zes at the end of the vertical movement 0 the switch G, having maintained the operating circuits of the main selector F open. After the im ulses to the vertical magnet 177 cease, the circuit through the winding of relay 171 is open at back contact of armature 91, relay 171 therefore deenergizes after an instant and com ,letes a circuit to the rotary magnet'178. agnet 178 operates to step onto the first also to open the locking circuit of the interrupter relay 172 which deenergizes and opens the circuit of the rotary magnet which deenergizes also. Now if the selector contacts is busy'a ground potential will be present on the test contact engaged by the test wiper 235. Then as soon as ma net 178 deener izes the circuit of relay 1 2 will again e closed from ground by way of the said test wiper, armature 299 and its back contact, interrupter sprin s 181, and then over the previousl traced circuit .throu h the winding of re ay 172 to battery T e relay 172 will again energize therefore to close the circuit of the rotary ma et at armature 21 9 and its front contact. he rotary magnet operates as before to step the wipfrs 235-238, inclusive, on to the next set of ank contacts and to 0 en the locking circuit of relay 172 which eener 'zes opening the rotaryv magnet circuit whic deenergizes also. This alternate operation of relay 17 2 and the rotary magnet 178 continues until an idle trunk is found which we will assume, is the trunk line comprising conductors 262, 263, 264, and 265, the test contact 268 ofwhich will be ungrounded and hence there will be no circuit for relay 172. The switching relay 169 which has hitherto been ound on the various short circuited by the energized as there test contacts will now with the first set of bank mess is no und potential on the test contact of an idle trunk line. The circuit for the energlzation of relay 169 extends from ground. on conductor 123 through the winding of relay 169, springs 181, thence over the previously traced circuit and through the winding of relay 172 to battery. Relay 169 is of such' high resistance that it alone will energize over the above traced circuit way of armature 92 and its front contact,

armature 77 and its resting contact, back contact and armature 72, conductor 127,

' armature 194 and its back contact, back contact and armature 199, front contact and armature 210, armature 233 and its back contact, through the windin of slow acting series relay 17 3, wiper 236, ank contact 269, conductor 263, armature 355 and its resting contact, and through the winding of the line relay 350'. of the selector I.

Relays 173 and 350', will energize over the circuit, relay 173 completing the circuit of slow acting relay 174 at armature221, and relay 350' completing the circuit of the slow acting release relay 351'. The calling subscriber at substation A may now operate his calling device for the next digit of the desired number thereby producin a series of interruptions in the circuit of t e line relay 56 of the main selector F which operates to repeat them to the line relay 350' of the selector Iover the previously traced circuit. The line relay 350 responds thereto, to control the operation of the vertical magnet 356' which operates to step thewi ers 359'362', inclusive, op osite the desir level of bank contacts. T e selector then rotates to find an idle trunk line in identically the same manner as the selector H operated, which operation was described full hereinbefore. Upon an idle trunk being so ected which, we will assume, is the trunk line comprising conductors 379'382, inclusive, the switching relay 354' will energize in the usual manner in series with the interrupter relay 353. On its energization, relay 354' disconnects the incoming dialing conductor.

the release trunk conductor 262 by way of front contact and armature 357 test wiper 359, bank contact 375', conductor 379', and

through the winding of'the slow acting release rela 401' to battery,

placing the busy tone on the upper line conductor 381 at armature 428' and at armature 426 opening the circuit to the line relay 400' of the connector K. The busy tone is audible to the calling subscriber over a circuit similar to the one hereinbefore traced, and upon hearing this tone the calling subscriber will hang up thereby releasing the operated switches in a manner similar to that hereinbefore described.

Assuming now that the second called subscribers line is idle, then as soon as relay 405' energizes the dialing conductor is opened as before at armature 425, and the ringing circuit is prepared .at armatures 42 and 429'. As before described, as soon as the circuit to the line relay 400' is broken the slow acting series relay 173 deenergizes completing relay 176 and at the same time places the connector cut on tone in the calling subscribers line for a short interval notifying him of the operation. Upon relay 176 energizing, the ringing circuit for the called subscriber is completed from the generator V and this current flows over a circuit similarto when the subscriber at substation P was signalled, through the ringer of called substation back through the lower winding of the ring cut off relay 175. When the subscriber answers the ring out ofi relay energizes over the line circuit and operates to cut off the ring and complete the circuit of the back bridge relay 165 which also energizes over a circuit including the called subscribers line loop. Upon energizing, relay 165 closes a circuit for the slow acting relay 166 which relay operates to prepare the operating circuits of the main selector F, completes the circuit of the slow acting relay 167 and also places ground on conductor 128 which extends through the winding of the reversing relay 25 to battery. This latter relay operates as before, toreverse the battery over the trunk line for any desirable purpose. Conversation may now be carried on between the two arties over the heavy line conductors. After this is terminated the connection may be released as before described by the calling subscriber replacing his receiver on the switchhook.

scriber for the calling the circuit for the wiper cut on v This passing scriber'ma be as desira 0 each, time releasing partyin the connection upon the of the next subscribers number if th'e cal ed.

continued indefinitel as lon' t e call party remains on the line. If however, the.

s up first a circuit for. the release magnet o the selector whichjs then in use is effective. Assuming the main selector F to be in use; when the called subscriber replaces his receiver on the switch hook the circuit of the back bridge-relay 51 is opened which relay deenergizes sending an impulse of current at armature to the slow acting relay 54 which energizes. circuit is now eifective extending from ground G", off normal spring 242 and its resting contact, conductor 148, front contact and armature 82, armature 74 and its back contact, ofi normal springs 117, and through the winding of release magnet 66 to battery. Magnet 66 operates, opening the operating circuits of the main selector as before and called subscriber han restores the switch F to normal. Now, if the calling subscriber should pass the call he will operate the main selector F again as in the case first described, all the apparatus being now in its original position.

It will now be assumed that the second called subscriber called through element G finds that it is necessary to call another subarty. Under these condltions the second ca led party will operate his calling device for the local subscribers number producing a number of series of interruptions in the circuit of the back bridge relay 165. When the second called subscriber operates his calling device for the first digit of the local number the back bridge relay 165 responds to the interruptions in its l1ne circuit and at each retraction of its armature 193 completes a circuit as follows: from ground G by way of armature 193 and its back contact, armature 202 and its front contact, conductor 133, through the winding of the slow acting-series relay 58, conductor 139, back contact and armature 215, conductor 141, armature 155 and its back contact, back contact and armature 89, and

through the winding of the vertical magnet.

64 to battery. The slow acting relay 168 energizes in multiple with the above traced circuit but at this time its operation will have no effect. Relay 185 also energizes in parallel with the relay 168 and being a. slow acting relay, maintains its armature attracted throughout each series of im ulses-serving to open the circuit to the line 0 the calling subscriber thereby preventing the dial impulses from causing him any annoyance. The slow acting series relay 58 also energizes in series with the vertical magnet circuit and maintains its armature attracted thoughout the vertical movement of the switch. Magnet 64 operates as before, to step'the wipers 112-115,

of the call'bythe calling sub- 'i n the selected level. Theinterrupter relay,

' of the rotary m op osite some level of bank contacts in which terminate trunk lines leadin to selector switches. As before describe upon the wipers leaving their normal position the ofi normal springs operate and a circuit is completed for the interrupter relay 69, which energizes, establishes a locking circuit for itself, and prepares the rotary magnet circuit. At, the'end of the vertical movement of the switch, relay 58 deenergizes completing the circuit of the rotary magnet 65 which operates to open the locking circuit of the interrupter relay 59 and to rotate the wipers 112-115, inclusive, into enagement with the first set of bank contacts inclusive,

of course, deenergizes, breaking the circuit et which also deenergizes. The trunk selecting operation will go forward in the manner reviously explalnednntil a trunk is found terminating in an idle selector switch which it will be assumed is the trunk line comprisin the conductors 250, 251, 252, and 253. en the switching relay energizes, upon an idle trunk line being found, a re eating circuit is completed extending as f0 ows: ground G, armature 92 and its front contact, armature 77 and its back contact, back contact and armature 72,

conductor 127, armature 194 and its front contact, front contact and armature 199,

conductor 121, front contact and armature 90, armature 158 and its back contact, through the winding of the slow acting relay 61, wiper 113, bank contact 258, conductor 251, armature 300 and its back contact, and thence through the winding of the line relay 301 of the selector H. he operation of this selector and the connector operated in response to the succeeding digits of a third called subscribers number will, of course,

be identical with that hereinbefore described. Should the second called party discover that he made an error in calling one of his numbers before sending the last digit or during its transmission he may re lace his receiver on thefswitchhook thereby reaking the circuit of the back bridge relay 165 which deenergizes. A circuit is then completed extending from ground G", ofi normal spring 118 and its working contact, armature 109 and its back contact, conductor 150, armature 203 and its front contact, back contact and- -armature 196, conductor 130, ofi normal springs 117, and through the winding of the release magnet 66 to battery. Magnet 66 operates in the usual manner to restore the main selector to normal after which the succeeding respect ve release magnets.

,However, if the second called subscriber completes the connection to the third called subsc'ribers line and should then desire to release in case the line is busy or the party called dont answer he may do so by dialing ate and the switch switches will be restored by their.

.maas

terruption m the. circuit of the back brid e relay 165 which 0 rates to send an impu of current to the s ow acting relay 168 in the usual manner. A circuit is then efiective extending as follows: from ground G" by way of armature 192 and its front contact, armature 205 and its front contact, conductor 151, armature 110 and its front contact, (relay 63 now being energized), ofi normal springs 117 and through t magnet 66 to batteriy. Ma et 66 will 0 rwill t en be restore to its normal position. The operated switches will then be restored to normal in a manner hereinbefore described.

It may sometimes happen under certain conditions that an impulse of current is sent to the vertical ma switches. It will assumed that an impulse of current has been sent to the vertical magnet of the main selector F. Under these conditions magnet 64 willoperate stepping the shaft up one step thereby causing the springs 119 to operate and upon the deenergization of the slow acting series relay 58 a circuit is completed extending from the dual switches next to be used to its normal condition because if the said one of the switches is normalit will step to the first level and releasefourw times responsive to the four digits. If 'in an operated position the selector then seized and thereafter a donnector will be operated, and finally a circuit will be completed for the release magnet of the operate dual switch in response to the next digit over one of the release circuits herein described so the said selector and connector will also be restored. Any subsequent di its I sent after the restoration of the switc es will operate the restored dual switch and thereupon restore it. That is, if four digits 1 are not required to link the connector to the called line terminals and restore it, the extra di 'ts I sent will have no linking efl'ect as the 51 181 switch element will opertaiie and release idly for each extra Ti; will now be assumed that the second called subscriber after completing the setting up of the connection to a. third partys line does not wish to hold the line until that party answers. He will therefore replace e winding of the release et of one of the dual the back bridge relay 7 165 is thereby broken and on its deenergiz'ation sends an impulse of currentto the slow acting. relay 168. A circuit is now effective for release ma net .179 of the auxiliary selector G exten ing from ground'G, through off normal spring 118 and its working contact, armature 109 and its front contact, conductor 149,,armature 204 and its front contact, armature 197 and its back contact, 011 normal springs 241, and then through the winding of the release. magnet 179 to battery. The magnet 179 will operate to restore the auxiliary selector G to normal after which the switches'K and I that maintained the connection to the second called subscriber will be released by the operation of their respective release magnets, In the meantime the signalling of the third called subscriber will be going on and uponan answer being obtained conversation between the original calling and third called parties may take place over the same switches that were operated in the first case described. After the conversation is terminated the release will take place in the usual manner upon the subscribers replacing their receivers upon the switchhooks.

This third called subscriber may pass the call to a fourth subscriber in a manner similar to that above described exceptthat the back bridge relay 51 will be operated in response to the various digits to controlthe operations of the auxiliary selector and the succeeding switches.

It will thus be seen that this passing of a call by either the calling or called subscriber may go on indefinitely and in each case only the two subscribers are in com-, munication at once. It may be desirable however to arrange this system so that the three subscribers may remain on the connection for a conference, in this case the key K associated with the dual switches is operated by some person say the exchange attendant. Now whenthe call is passed by a called subscriber the three parties may remain inon the connection. The operation of the system in this case will now be briefly described.

For the purposes of this description it will be assumed that a calling main exchange subscriber at substation A has called a branch exchange subscriber at substation P by means of the main selector F and the succeeding switches in a manner similar to that hereinbefore explained, and that the subscriber thereat has responded and has extended the connection to the line of another branch exchange subscriber. such as the one at substation 0 through the medium of the auxiliary selector G and the switches I and K. The subscriber at the substation Q will be rung in the ordinary manner and that subscriber upon removing his receiver from the switchhook will stop the ringin operation and complete the circuit of the ackbridge relay "165 as described hereinbefore. Upon energizing, relay 165 will close the circuit of the slow acting relay 166 through the'key spring 120 and its working contact and.

hence the release circuit through" the contacts of the. slow acting relay 52 is inefiective. The three parties may now converse as .long as desired. If at any time one of the branch exchange subscribers, the. one at substation P for example should desire to talk to the calling subscriber alone he will simply operate his calling device for the digit 1...

thereby producing one interruption in the circuit of his back bridge relay 51. Upon theretraction of armature 70, slow-releasing relay 54 will actuate, so when armature 71 retracts a circuit may be traced from ground G? by way of armature 71 and its front contact, armature 84 and its front contact, conductor 135, armature 229 and its front contact, off normal spring 241, and thence through the winding of the release magnet 179 to battery. Magnet 179 operates to restore the auxiliary selector G to normal after which the selector I and connector K will be released. It will be seen that the subscriber at substation 0 could have released the subscriber at substation P in a similar manner by dialing 1. This circuit would extend from ground G, by way of armature 192 and its front contact, armature 205 and its front contact, conductor 151, armature 110 and its front contact, oflf normal springs 117 and thence through the winding of the release magnet 66 to battery. 'In this manner the system may be arranged so that the three subscribers may remain on the connection and at the same time providing means so I armatures opening the operating circuits= of that switch. This locking circuit of the release magnet will be effective until all the impulses of the digit called to release have ceased for the reason that one slow acting series relay will be energized locking the release magnet in an obvious manner.

Under certain conditions it might be desirable to arrange groups of telephones under one number and if one of these were busy the other would be selected automatically. The connectors J and K have also been designed to serve this class of subscribers. To arrange the connector J to serve this class of subscribers the tie between the two test or private bank cont-acts such as 381 and 

